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#ifndef _FAST_INTERSECTOR_H_
#define _FAST_INTERSECTOR_H_
#include <memory>
#include <unordered_map>
#include <vector>
#include <boost/functional/hash.hpp>
using namespace std;
namespace extractor {
typedef boost::hash<vector<int>> VectorHash;
typedef unordered_map<vector<int>, vector<int>, VectorHash> Index;
class Phrase;
class PhraseLocation;
class Precomputation;
class SuffixArray;
class Vocabulary;
/**
* Component for searching the training data for occurrences of source phrases
* containing nonterminals
*
* Given a source phrase containing a nonterminal, we first query the
* precomputed index containing frequent collocations. If the phrase is not
* frequent enough, we extend the matchings of either its prefix or its suffix,
* depending on which operation seems to require less computations.
*
* Note: This method for intersecting phrase locations is faster than both
* mergers (linear or Baeza Yates) described in Adam Lopez' dissertation.
*/
class FastIntersector {
public:
FastIntersector(shared_ptr<SuffixArray> suffix_array,
shared_ptr<Precomputation> precomputation,
shared_ptr<Vocabulary> vocabulary,
int max_rule_span,
int min_gap_size);
virtual ~FastIntersector();
// Finds the locations of a phrase given the locations of its prefix and
// suffix.
virtual PhraseLocation Intersect(PhraseLocation& prefix_location,
PhraseLocation& suffix_location,
const Phrase& phrase);
protected:
FastIntersector();
private:
// Uses the vocabulary to convert the phrase from the numberized format
// specified by the source data array to the numberized format given by the
// vocabulary.
vector<int> ConvertPhrase(const vector<int>& old_phrase);
// Estimates the number of computations needed if the prefix/suffix is
// extended. If the last/first symbol is separated from the rest of the phrase
// by a nonterminal, then for each occurrence of the prefix/suffix we need to
// check max_rule_span positions. Otherwise, we only need to check a single
// position for each occurrence.
int EstimateNumOperations(const PhraseLocation& phrase_location,
bool has_margin_x) const;
// Uses the occurrences of the prefix to find the occurrences of the phrase.
PhraseLocation ExtendPrefixPhraseLocation(PhraseLocation& prefix_location,
const Phrase& phrase,
bool prefix_ends_with_x,
int next_symbol) const;
// Uses the occurrences of the suffix to find the occurrences of the phrase.
PhraseLocation ExtendSuffixPhraseLocation(PhraseLocation& suffix_location,
const Phrase& phrase,
bool suffix_starts_with_x,
int prev_symbol) const;
// Extends the prefix/suffix location to a list of subpatterns positions if it
// represents a suffix array range.
void ExtendPhraseLocation(PhraseLocation& location) const;
// Returns the range in which the search should be performed.
pair<int, int> GetSearchRange(bool has_marginal_x) const;
shared_ptr<SuffixArray> suffix_array;
shared_ptr<Vocabulary> vocabulary;
int max_rule_span;
int min_gap_size;
Index collocations;
};
} // namespace extractor
#endif
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